Method in shaping a solid body against another body



April 1946- N. G. ELFSTRC'jM 4 2,398,364

METHOD IN SHAPING A SOLID BODY AGAINST ANOTHER BODY Filed May 26, 1943 ATTORNEYS Patented Apr. 16, 1946 CFFICE Mn'rnop 1N SHAPING A soup BODY AGAINST ANOTHER BODY Nils Gustaf Elfstrom, Fagersta, Sweden Application May 26, 1943, Serial No. 488,559 In Sweden March 17, 1942 6 Claims. (Cl. 29-1495) Products manufactured through powder metallurgy, i. e, of metal powder by a sintering process, often cannot be obtained with the desired exact dimensions by sintering only, Therefore, the sintered body is usually subjected to a calibration consisting of shaping by pressing or hammering against the resistance of a shaping body. Further, the shape which one desires to give to the body is sometimes such that the same cannot be obtained completely during the pressing operation which usually precedes the sintering or is effected simultaneously therewith since, for example, the body could not then be removed from the press mould. The shaping required in this case can often be completed during the calibration particularly as sintered bodies are usually rather porous.

The object of the present invention is to obtain a certain clearance between a forming body and the formed body at such calibration. This is carried out in such a way that that body which is surrounded by the other body is given a higher temperature, and consequently (at positive coefficient of thermal expansion) has a larger volume in comparison with the latter body than if both of them had the same temperature. If the body in question cannot be heated, or if the possible heating is insufficient to obtain the desired clearance, the temperature difference can be obtained, or increased, by cooling the surrounding body.

One example of the use of the method is the calibration of self-lubricating bearing bushes produced through powder metallurgy, for example by pressing or hammering around a mandrel. The method according to the present invention now makes it possible to use one and the same mandrel as the shaping body during the calibration of bushes with somewhat different inside diameters; Further, by means of the method the shaft for which the bearing is intended can be used as the shaping body or mandrel. It is already known to obtain a clearance by utilizing the thermal expansion, namely by using two materials with very different coefficient. of thermal expansion, such as metal and artificial resin.

However, in contradistinction to the method according to the present invention, the two elements in the prior instance referred to have the same temperature during the shaping. In bearings of the kind in question it is further known to obtain the clearance through a movement enforced on either or both of the sliding elements. However, if in the method according to my invention a movement is simultaneously enforced on the sliding elements, said movement is not liable to favour the creation of clearance but, on the contrary, acts in itself to close the existing clearance. The present method has for its purpose to restrict said action.

The method according to the present invention may be illustrated by the following example and the annexed drawing forming part of this specification.

In the drawing:

- Figs. 1 and 2 show longitudinal sections through a shaft and a bushing in various steps of the method of this invention.

The shaft is designated by a, the bushing by b. c is a compressing tool.

The previously manufactured bushing b is loosely fitted on shaft a, the shaft being heated or the bushing cooled, or both, and a compressing tool 0 is applied for compressing the bushing on the shaft so that the interior surface of the bushing is shaped in conformity with the surface of the shaft. v Y

On completion of the shaping process and restoring of normal temperature and volume of the body or bodies, which had been submitted to a change of temperature, a clearance will have formed between both bodies.

If, for example, in a 15 mm. shaft of steel having the thermal expansion coeflicient 0.000012 a clearance of 0.02 mm. between the shaft and the bearing bush is desired, the shaft is allowed to have a temperature of 240 C. at the calibration whereas the bush has room temperature 20 C. Should the steel in the shaft not bear heating to such temperature that the temperature of the shaft is 240 C. at the calibration, the required temperature differential may be obtained by cooling the bush. For example, the bush may be cooled by carbon dioxide snow and have a. temperature of -20 C. at the shaping, in which case the temperature of the shaft only need amount to 200 C.

The above described possibility of using the shaft itself as a calibrating mandrel has proved particularlyvaluable in the manufacture of selflubrlcating and self-adjusting sliding-friction bearing units consisting of two sliding elements with mutually cooperating spherical sliding surfaces. I have used a sintered hollow cylindric bush of self-lubricating material soaked with oil and a steel ball provided with a. cylindric hole,

the outside diameter of which ball is somewhat less than the inside diameter of the bush. The steel ball is heated in an oil bath, and simultaneously the sintered bush is cooled by carbon dioxide snow. if required. At the calibration the hot ball is quickly inserted into the cool, or possibly cooled, bush, and both are pressed through a calibrating matrix. By this means the sintered bush is pressed around the steelball so that the interior surface of the bush becomes spherical. Thus, the two elements are combined into a unit, and after equalization of the temperature a clearance is obtained between them, the size of which is conditioned by the temperature difference.

Although the cited example applies to products of powder metallurgy, the method may of course equally be used where a clearance is desired between other bodies which can be shaped against one another by a pressing or hammering method.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a method of forming a unit of an outer body and an inner body, both contacting each other with their interior and exterior surfaces, respectively, said inner body adapted to be moved within said outer body, the steps of loosely fitting said outer body of solid material around said inner body, employing said inner body as a core or mandrel and applying external pressure to cause said outer body at its contacting surface to assume the shape of the contacting surface of said inner body whilst submitting said bodies to a temperature differential by applying to at least one of said bodies a temperature change to keep said outer body at a lower temperature than said inner body and to cause a volume change of said body submitted to said temperature change so as to stress and urge the contacting surface of said body towards the contacting surface of the other of said bodies and, on completion of the shaping process and equalization of the temperature of said bodies, to re move said contacting surfaces from one another and cause a clearance therebetween.

2. A method of applying a separately manufactured solid bushing to a metal shaft, comprising loosely fitting said bushing around said shaft, applyin external pressure to said bushing to cause said bushing at its interior surface to be shaped in conformity with the surface of said shaft whilst submitting said shaft and bushing to a temperature differential by applying heat to said shaft to expand same and stress and urge its surface against the inner surface of said bushing during said shaping process, and, on completion of said shaping process, restoring normal temperature and volume of said shaft thereby forming a clearance between said shaft and said bushing.

3. A method .of applying a separately manufactured solid bushing to a metal shaft, comprising loosely fitting said bushing around said shaft, applying external pressure to said bushing to cause said bushing at its interior surface to be shaped in conformity with the surface of said shaft whilst submitting said shaft and bushing to a temperature difierential by cooling said bushing to contract same and stress and urge its interior surface towards the surface of said shaft during said shaping process, and, on completion of said shaping process, restoring normal temperature and volume of said bushing thereby forming a clearance between said shaft and said bushing.

4. A method as claimed in claim 1 wherein the said temperature change is effected by heating the body serving as a mandrel to such an extent as to cause expansion thereof while maintaining the other body at room temperature.

5. A method as claimed in claim 1 wherein the temperature change is effected by cooling the body to be shaped sufiiciently to contract it while maintaining the other body at room temperature.

6. A method as claimed in claim 1 wherein the temperature change is efiected by cooling the body to be shaped and heating the other body.

NILS GUSTAF ELFSTROM. 

